On days with high numbers of birds, we don’t usually have enough time to photograph certain species, sexes, or ages for comparisons. But, when two male Black-throated Blue Warblers of two different ages come in at the same time, we can’t pass on the opportunity to compare molt and plumages!
Juvenal feathers are grown quickly and at all once in the nest, resulting in a feather of lesser quality and density that is more susceptible to the elements as compared to a basic feather. Evident in our two BTBWs, the SY bird shows juvenal primary coverts, primaries, secondaries, and tertials that are fairly dull and gray, with limited greenish edging, and contrast with the more recently replaced blue edged, dark centered greater coverts. The ASY bird’s wing shows covert and flight feathers of a single generation that all have a glossiness to them (on account of the more densely barbed feathers), dark gray to black centers, and blue edges (especially in the greater coverts and tertials). Due to this obvious difference between matte gray and dark black, and green versus blue, male Black-throated Blue Warblers are a great bird for learning about molt. This difference is so obvious it can even be viewed through the binoculars in the field!